The low-power design of LoRa terminals has always been a topic of concern in the industry. At present, the IoT industry generally claims that the battery life of loRa can reach more than 10 years. However, in actual products, since the standby time and working mode have a great influence on power consumption, the difference in standby time is also relatively large. For LoRa products with relatively low frequency of use, the standby time can reach 3-5 years, but for some LoRa products with GPS real-time tracking, the battery may only have a few days of life. Therefore, for actual Lora terminal products, how to reduce its power consumption, extend the actual standby time as much as possible, and reduce the frequency of maintenance to reduce costs, still needs to focus on.
To realize the low-power design of the LoRa terminal, it is necessary to understand the current consumption characteristics of the different working stages of the LoRa terminal.
The working phases of common LoRa terminals with sensors can be roughly divided into: standby/sleep phase, sensor acquisition phase, data sending phase, and data receiving phase.
Let's take the LoRa temperature and humidity sensor composed of RAK4200+SHTC3 as an example to actually experience the power consumption characteristics of the LoRa terminal in the above four working stages.
(Picture 1) LoRa terminal RAK4200 temperature and humidity sensor power consumption
Figure 1 is the LoRa temperature and humidity sensor composed of RAK4200+SHTC3 wakes up from the dormant state, collects data, sends data to the current change in the dormant state again.
(Picture 2) LoRa terminal RAK4200 temperature and humidity sensor power consumption
Figure 2 shows the current change when the LoRa temperature and humidity sensor composed of RAK4200+SHTC3 sends data to receive data, and enters the sleep state again.
According to Figure 1 and Figure 2, we can see the characteristics of current consumption in different working stages:
Standby/sleep phase
The standby/sleep phase corresponds to the phase when the sensor is not working. In this phase, there is the static power consumption of the LoRa terminal, that is, the standby/sleep power consumption. The characteristic of the current consumption in the standby/sleep phase is that the current consumption per unit time is small, but the time in this state is long. Therefore, reducing the standby current can effectively reduce the power consumption of the LoRa terminal.
RAK4200 series products use ST's low-power MCU, which can make the node not collect and transmit data, and the standby current can be reduced to 4uA. This means that a 2000mAh battery can theoretically make the RAK4200 node that sends data stand by for more than 50 years. (Without considering battery self-loss)! It can be seen that when the standby current drops to uA level, the standby current is no longer the main factor affecting the battery life of the LoRa terminal.
In the
LoRa terminal in the sensor acquisition phase, the power consumption of the sensor acquisition phase is mainly affected by the sensor's own warm-up power consumption, working power consumption and time, and MCU working power consumption. In this case, due to the relatively small operating current of the SHTC3 used, the main power consumption of the sensor acquisition phase is the operating power consumption after the MCU wakes up, which is about 10mA and lasts about 20ms.
Data transmission stage
As can be seen from Figure 1 and Figure 2, the stage where the current is the largest, which is the maximum power consumption of the LoRa terminal, is the stage of sending data . This stage consumes the most power. In LoRa terminal products, the maximum transmission current can reach 120mA or more. , The maximum duration can exceed 2s, and the maximum power consumption per packet can be up to 0.3mWh. Similarly, for a 2000mAh battery, it can only support such a package to send less than 30,000 times.
In the receiving data stage,
in the LoRa sensor network, if the node opens the confirmation frame setting, the receiving window will be opened to receive the confirmation frame 1s after the end of the transmission. After the data is sent, the current waveform changes in the receiving window. As can be seen from the second picture above, the current in the receiving phase is much smaller than that in the transmitting phase. Because the confirmation frame is relatively short and the duration is relatively short, generally receiving The power consumed during the data phase is about 10% of the power consumed during the data sending phase.
Therefore, the low power consumption design of the LoRa terminal can be carried out from the following aspects to prolong the service life of the battery.
Reduce standby power consumption
Although the standby power consumption is the lowest among the 4 working stages of the LoRa terminal, the standby stage generally lasts significantly longer than other stages. Therefore, reducing the standby power consumption can significantly reduce the power consumption of the LoRa terminal.
In this regard, RAK has completed the low-level low-power design in the software and hardware of LoRa terminal products, which can reduce the standby current of LoRa terminal products to 4uA. Thus, in theory, the RAK4200 node that sends data can be on standby for more than 50 years !
Reduce the power consumption of sending data
Among the 4 working stages of the LoRa terminal, the data sending stage consumes the most power per unit time. Under the premise that the standby power consumption has been reduced to a low level (for example, the standby current of RAK4200 RAK4200 is 4uA), the standby power consumption can be ignored at this time. Then, the main factor affecting the battery life is the consumption when sending data的current. Therefore, reducing the power consumption of sending data can effectively reduce the power consumption of the LoRa terminal.
To achieve the reduction of power consumption for sending data, you can proceed from three aspects.
(1) The number of transmissions can be reduced and the transmission interval can be increased to effectively reduce the power consumption of the LoRa terminal and extend the battery life of the LoRa terminal.
(2) ADR technology can be used.
The Adaptive Data Rate (ADR) related operations are defined in the LoRaWAN protocol, which enables the terminal node to select the optimal transmission rate and the lowest output power, that is, when the signal is good, the transmission power can be automatically reduced, thereby reducing power consumption. Extend battery life.
We ADR process RAK4200 network and dynamically adjusted, can clearly see, the termination node function LoRa consumption have been significantly reduced.
(Picture 3) LoRa terminal RAK4200ADR network access packet current
Figure 3 shows the process of an ADR-enabled node of RAK4200 from entering the network to normal packet sending. The horizontal axis is time, and the vertical axis is the current consumption of the module. When the module first entered the network, the current when sending the package exceeded 120mA. Starting from the third message, the node gradually reduces its output power, so the current also drops significantly. After 5 or 6 packet adjustments, the current value has dropped to about 60mA, and the message that this node reaches the gateway can still maintain a high SNR.
If there is no ADR adjustment, a 2000mAh battery can transmit about 40,000 packets. If the ADR function is used, it can transmit about 2.2 million packets, which is a 55-fold increase! Thus, the power consumption of the LoRa terminal can be greatly reduced.
(3) If it is not necessary, you can turn off the confirmation frame function.
When using sensors, choose low-power sensors
Choosing a sensor with low power consumption will reduce the power consumption of data collected by the sensor, thereby reducing the overall power consumption of the LoRa terminal.
In the WisBlock series of products, RAK has also selected a series of low-power MEMS sensors to reduce the power consumption of LoRa terminals for customers to choose from.
In summary, for ordinary users, when using LoRa terminal products to achieve their own purposes, if they want to reduce power consumption, thereby extending battery life and reducing maintenance frequency, then, first of all, you can choose a lower standby power consumption Development board , secondly, you can choose products that use ADR technology, and finally, sensors with low power consumption should be selected as much as possible.